While I defend the form of the proposed #asPlural method against
the "asXXX should mean that XXX is a class" canard,
I would point out that there are languages with more than two numbers.
Singular, dual, plural is fairly popular, and
singular, dual, paucal, plural is not unheard of.
It would have to be
(aString) inflectedForNumber: (anInteger)
which would also solve the -ise/-ize problem.
Of course, there are the languages where the dual is used for objects
that *naturally* come in pairs (scissors, trousers, &c) while the plural
is used for 2 of other things, so ...